Preeclampsia is a syndrome characterized by hypertension and proteinuria. The aim of this study is to find the relationship between preeclampsia, asymmetric dimethyl arginine (ADMA), and the oxidant/antioxidant system. Twenty-one preeclamptic and 28 normal pregnant women were included in this study. In cord bloods, ADMA and oxidant/antioxidant parameters were measured. Asymmetric dimethyl arginine levels were significantly increased in preeclamptic pregnancies compared to the control group (p = 0.006). The activities of antioxidant enzymes and malondialdehyde levels were increased in the preeclamptic group compared to the control group (p < 0.001, p = 0.022, p < 0.001, p < 0.001, respectively). Development of endothelial dysfunction and oxidative stress may play a role in developing preeclampsia.